KAP140 Autopilot Details

"Dave Butler" wrote in message
...
Peter R. wrote:
Dave Butler ) wrote:


I assume you meant "...to match your current heading".


Yes.


directs the AP to turn in the direction you turned the heading bug,
away
form the desired course. Left alone, the AP will soon turn back and
re-
intercept the desired course.

If you turned the heading bug in the direction to match your current
*heading*,
and and the AP turns in the direction you turned the heading bug, That
turn will
be *toward*, not away from the desired course.


No, that is not what I am saying. The AP is already tracking the
current
course, which results in maintained heading. However, the heading bug
happens to be five degrees to either side of the current heading. This
could either be because of a crosswind or perhaps DG precession.

If the pilot moves the heading bug to match the current heading, which
is
also the course being tracked by the AP, the AP momentarily turns *away*
from the desired course.

OK, I don't want to beat this greasy spot where there used to be a dead
horse,
but I think it's important that we not misinform someone who might be
reading
this and trying to learn from it.

What you are saying may be correct, if it's behavior peculiar to the
KAP140. It
is definitely counter-intuitive to me, and not the way APs that I have
used behave.

Maybe we're just tripping over imprecise use of terminology, so let's be
very
precise in the words we use. Sometimes an example is easier to understand
than
just discussing the principle in the abstract, so permit me to concoct an
example.

Example: We want to follow an airway that goes TO a navaid along that
navaid's
180 radial. That is, the desired course is 360, along the 180 radial from
the
navaid. There is a wind from the west. The DG and the magnetic compass
have been
adjusted so that they are in agreement.

We manually (no autopilot) maneuver the aircraft so that it is centered on
the
180 radial and heading 360. The OBS is set to 360, and the heading bug is
set to
360. The CDI is centered. Now turn on the autopilot.

So far you have set up to fly a ground station based on radio magnetic
course angle.

The heading is 360, but the wind from the west results in a track of (say)
010.
The CDI starts moving to the left as we drift off the desired track to the
right. The autopilot responds to the left-moving CDI by changing the
heading to
the left, say 350.

Now you use the tern "track", which is Long Range Nav; such as GPS, et al.
Track is a position displacement system and different from an angle.